[MLIR][Standard] Implement constant folding for IndexCast

[merge_guards_bot]

Unit tests: pass. 62315 tests passed, 0 failed and 838 were skipped.

clang-tidy: fail. clang-tidy found 0 errors and 1 warnings. 0 of them are added as review comments below (why?).

clang-format: fail. Please format your changes with clang-format by running git-clang-format HEAD^ or applying this patch.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

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[merge_guards_bot]

Unit tests: pass. 62315 tests passed, 0 failed and 838 were skipped.

clang-tidy: fail. clang-tidy found 0 errors and 1 warnings. 0 of them are added as review comments below (why?).

clang-format: pass.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

Pre-merge checks is in beta. Report issue. Please join beta or enable it for your project.

[rriddle]

mlir/lib/Dialect/StandardOps/Ops.cpp

1605

Few nits:

• Can you use a more descriptive name than 'a'? e.g. 'value'?
• Merge the variable into the if condition.

1611

nit: Why not just Attribute?

mlir/test/Transforms/canonicalize.mlir

897

Please follow the testing guidelines(e.g. don't capture SSA values directly):

https://mlir.llvm.org/getting_started/TestingGuide/

[merge_guards_bot]

Unit tests: pass. 62518 tests passed, 0 failed and 844 were skipped.

clang-tidy: pass.

clang-format: fail. Please format your changes with clang-format by running git-clang-format HEAD^ or applying this patch.

Build artifacts: clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

Pre-merge checks is in beta. Report issue. Please join beta or enable it for your project.

[stephenneuendorffer]

Any more comments?

[rriddle]

Sorry for the delay. I was waiting for you to mark the comments as Done before returning to the review.

mlir/lib/Dialect/StandardOps/Ops.cpp

1594

Can you merge this variable into the if condition?

(Can you resolve this?)

mlir/lib/Dialect/StandardOps/Ops.cpp

return (a.isIndex() && b.isa<IntegerType>()) ||
          (a.isa<IntegerType>() && b.isIndex());
 }
 
 OpFoldResult IndexCastOp::fold(ArrayRef<Attribute> cstOperands) {
   // Fold IndexCast(IndexCast(x)) -> x
   auto cast = dyn_cast_or_null<IndexCastOp>(getOperand().getDefiningOp());
   if (cast && cast.getOperand().getType() == getType())
     return cast.getOperand();
+
+  // Fold IndexCast(constant) -> constant
+  // A little hack because we go through int.  Otherwise, the size
+  // of the constant might need to change.
+  if (auto value = cstOperands[0].dyn_cast_or_null<IntegerAttr>())
+    return IntegerAttr::get(getType(), value.getInt());
+
   return {};
 }
 
 //===----------------------------------------------------------------------===//
 // LoadOp
 //===----------------------------------------------------------------------===//
 
 static void print(OpAsmPrinter &p, LoadOp op) {
   p << "load " << op.getMemRef() << '[' << op.getIndices() << ']';
   p.printOptionalAttrDict(op.getAttrs());
   p << " : " << op.getMemRefType();
 }
 
 static ParseResult parseLoadOp(OpAsmParser &parser, OperationState &result) {
   OpAsmParser::OperandType memrefInfo;
   SmallVector<OpAsmParser::OperandType, 4> indexInfo;
   MemRefType type;
 
   auto indexTy = parser.getBuilder().getIndexType();

mlir/test/Transforms/canonicalize.mlir

 // CHECK-LABEL: func @index_cast
 // CHECK-SAME: %[[ARG_0:arg[0-9]+]]: i16
 func @index_cast(%arg0: i16) -> (i16) {
   %11 = index_cast %arg0 : i16 to index
   %12 = index_cast %11 : index to i16
   // CHECK: return %[[ARG_0]] : i16
   return %12 : i16
 }
+
+// CHECK-LABEL: func @index_cast_fold
+func @index_cast_fold() -> (i16, index) {
+  %c4 = constant 4 : index
+  %1 = index_cast %c4 : index to i16
+  %c4_i16 = constant 4 : i16
+  %2 = index_cast %c4_i16 : i16 to index
+  // CHECK: %[[C4_I16:.*]] = constant 4 : i16
+  // CHECK: %[[C4:.*]] = constant 4 : index
+  // CHECK: return %[[C4_I16]], %[[C4]] : i16, index
+  return %1, %2 : i16, index
+}